1. Field of the Invention
The present invention relates to an estimation method for floor reaction forces acting on a two-legged walking mobile body such as a human being.
2. Related Background Art
For example, when applying support torques to joints of each leg of a two-legged walking mobile body such as, for example, a human being to assist a walking motion of the two-legged walking mobile body, there is a need to estimate moments, which should be generated at the joints of the each leg (joint moments required for the motion of the two-legged walking mobile body). Moreover, to estimate the joint moments, it is required to grasp floor reaction forces (vectors) acting on each landing leg. The term “floor reaction force” is accurately a vector quantity composed of a translational force and a moment. It is assumed, however, that the “floor reaction force” in this specification means a vector of the translational force.
As a method of estimating the floor reaction force, there is, for example, an already known method suggested by this applicant in Japanese Patent Laid-open No. 2003-89083 (hereinafter, referred to as the patent document 1). In this method, an acceleration (vector) of a center-of-gravity of a two-legged walking mobile body is calculated by using an output of an acceleration sensor attached to the waist of the two-legged walking mobile body or outputs of joint displacement sensors for detecting displacements (rotation angles) of joints (hip joints, knee joints, and ankle joints) of the legs, and then the total floor reaction force (vector), which is a total sum of all floor reaction forces acting on the two-legged walking mobile body, is calculated from the acceleration of the center-of-gravity and the weight of the two-legged walking mobile body. Thereafter, in the two-leg supporting state (during the period in which both legs are landing) of the two-legged walking mobile body, supposing that the floor reaction force acting on each leg is in the direction from the ankle joint of the leg to the center-of-gravity of the two-legged walking mobile body, the floor reaction force acting on the each leg is estimated in such a way that the total sum (vector sum) of the floor reaction forces acting on both legs equals the total floor reaction force. On the other hand, in the one-leg supporting state (during the period in which only one of the legs is landing), the total floor reaction force is estimated as a floor reaction force acting on the landing leg directly. The estimated value of the floor reaction force acting on the leg not landing is naturally zero.
This type of estimation method for the floor reaction forces is advantageous in that the floor reaction forces can be estimated without the attachment of a force sensor to the two-legged walking mobile body or installation of a force plate (a plate for detecting a load) on the floor.
In the technology disclosed in the patent document 1, the direction of the floor reaction force acting on the each leg is determined by the relative positional relationship between the center-of-gravity of the two-legged walking mobile body and the ankle joint in the two-leg supporting state of the two-legged walking mobile body. On the other hand, in the one-leg supporting state, the direction of the acceleration of the center-of-gravity of the two-legged walking mobile body calculated by using the output of the acceleration sensor is directly determined as the direction of the floor reaction force acting on the landing leg. Therefore, how to determine the direction of the floor reaction force acting on the each leg in the two-leg supporting state is different from the one-leg supporting state. Therefore, the direction of the estimated value of the floor reaction force acting on the each landing leg sometimes varies in a discontinuous manner at shift from one-leg supporting state to another supporting state. Particularly, the output of the acceleration sensor in the forward/backward direction (an acceleration detected value in the forward/backward direction) of the two-legged walking mobile body is susceptible to change in the direction due to an influence of a disturbance or the like, and thus an estimated value of an anteroposterior component of the two-legged walking mobile body has sometimes changed suddenly in a discontinuous manner in the floor reaction force acting on the each landing leg.
Moreover, in the one-leg supporting state, the output of the acceleration sensor is directly reflected on both the estimated magnitude and direction of the floor reaction force. Therefore, particularly in the one-leg supporting state, the direction of the estimated value of the anteroposterior component of the floor reaction force acting on the landing leg has been sometimes reversed in a fluctuating manner.
Therefore, in the technology disclosed in the patent document 1, it may be sometimes impossible to obtain such an estimated value of the floor reaction force that varies smoothly and continuously. Consequently, when estimating the joint moment by using the estimated value of the floor reaction force, the estimated value of the joint moment also has sometimes changed suddenly in a discontinuous manner or frequently changed in a fluctuating manner.